1. Field of the Invention
This invention generally relates to a fuse that can be re-set, and more specifically to a fuse having a plurality of fuse elements which can be moved into position between fuse leads to re-set a fuse.
2. Related Art
Fuses are a necessary component of many electrical systems. Fuses maintain the safety of a circuit by physically opening themselves to interrupt the flow of an electrical current whenever an excessive electrical current has been detected. In prior inventions, the detection of an excessive electrical current was accomplished by means of a fuse filament which was designed to melt in response to the heat produced by an excessive electrical current. This excessive current may exist because too many electrical devices or appliances are operating as to create excessively low resistances within the circuit, thereby risking the hazard of a fire.
Because of their simplicity of design and operation, many varieties of fuses can be mass produced at low cost, thereby providing an inexpensive means to ensure circuit safety.
However, there are disadvantages when maintaining safety through the use of fuses. Paramount is that fuses do not replace themselves. Unlike a circuit breaker, which need only be reset after the unsafe electrical condition has been abated, once a fuse has burned out, it remains lodged within the circuit requiring a person to perform a manual and tedious chore to remove the opened fuse and reinsert another entirely new fuse of like size, specification and capacity. Often this task of replacement requires the use of tools. If tools are not used, and sometimes even if they are, there is a risk to the person replacing the fuse of electrical shock as his or her skin might come into contact with a powered circuit.
Furthermore, fuse replacement is often made more aggravating by the fact that the open fuse must first be located among many similar fuses which are still in working order. Typically, all of the fuses for a system are grouped together within a single cabinet known as a "fuse box." Because fuse boxes are not pleasing to the eye, they are often installed within locations that are not conveniently or directly accessible to the consumer of electrical power. Once located, the consumer finds the fuse box to be packed with many identical or near identical fuses that are positioned in an arrangement that obscures the identity of the particular fuse which is in non-working order.
Accordingly, to locate the opened fuse, a person must use a chart to identify the component or circuit that has discontinued operating, and then match the chart against the arrangement of fuses within the fuse box to locate the non-working fuse. As one might expect, such a search for a blown fuse is much more difficult to perform if conducted in the absence of adequate lighting.
Also, since fuses blow at times that are inconvenient to the user, there exists a need for a storage device by which a replacement fuse element can be housed in a position that is electrically insulated from the circuit it is later to protect, but close enough to its future operating site that the consumer of electrical power does not have to conduct a rambling and disorganized search, often at a relatively remote location from the fuse box, for a compatible replacement fuse.
Ideally, it would be preferable if the replacement fuse element could be inserted into the circuit without the need for actual physical contact with the installer. In other words, to quickly move the fuse element from its storage position directly into the circuit to be protected. Such an system of replacement would eliminate nearly all of the tediousness and inconvenience that arise during the time of replacement.
Furthermore, such a system could abate the need for using an entirely new fuse to replace a blown fuse. Rather, only a component of the fuse, the fuse element, would need to be replaced.
Examples of previous efforts at re-settable circuit protection devices include:
Ahuja, U.S. Pat. No. 5,388,022 discloses an auto-rest circuit breaker having at least one solid state switch ( e.g. a triac, SCR or complimentary FET) that is biased to be normally closed and mounted in series with a shunt resistor or shunt resistor network. The shunt resistor creates a drop in voltage that is continuously measured, and may be converted from an analog to a digital value, to protect the circuit within the line from over-voltage or over-current conditions. Not relying upon thermal or electromagnetic relays, the circuit breaker provides instantaneous protection at an electronic speed.
Kowalski, U.S. Pat. No. 5,442,589 discloses a fuse circuit having a single physical fuse that is to be electrically blown and a non-volatile memory cell which confirms the condition of the fuse by measuring the current though a transistorized current divider network. Detection of a blown fuse is accomplished in the following manner: in the intact state, the low resistance of the fuse causes the current to bypass a parallel mounted transistor circuit and electrical ground. Should voltage overload conditions cause the fuse element to deteriorate, the resulting high resistance of the open fuse causes the current to reach electrical ground via the lower resistance path of the transistor circuit. The transistor circuit is preferably an Electrically Erasable Programmable Read-Only Memory (EEPROM) type floating gate transistor that is made of technology similar to that of the fuse.
Swensen, U.S. Pat. No. 5,420,561 discloses a circuit breaker or re-settable fuse device having a normally relaxed shape memory wire which receives heat from a resistor. Under prolonged overload current conditions, the resistor generated heat causes the shape memory wire to contract and shift a moveable terminal out of contact with a fixed stationary terminal, thereby interrupting electrical current in the circuit to be protected. Only when the overload conditions are removed does the current though the resistor drop to a point where the resultant heat is insufficient to maintain the contracted condition of the shape memory wire. The breaker or fuse thereby automatically resets itself.
Ball, et al., U.S. Pat. No. 5,409,402 discloses a device that houses a conventional fuse and permits installation without the use of tools. The interior of the rigid housing contains a pair of terminals and a fuse element that is positioned between these terminals by electrical contacts. Attached to the exterior of the housing are two plug portions, each of which extend in opposite axial directions, that are shaped for insertion and retention within the fuse socket. By removing or inserting the plug portion, the fuse is removed or installed within the circuit to be protected.
Canada, et al., U.S. Pat. No. 5,404,049 discloses a fuse blow circuit. The circuit includes an address buffer incorporated within a VLSI (Very Large Scale Integrated) semiconductor chip, which makes use of its existing input/output pads that are dedicated to other circuit functions, to determine the condition of fuses. Also included are a fuse latch chip, a fuse blow chip and a fuse sense chip. These three chips are required for each fuse used. A fuse control circuit is included and may be shared for a bank of fuses. The fuse sense circuit continuously tests a fuse by measuring a voltage drop across a resistor that receives a trickle current from a transistor. If an excessively high voltage opens a fuse element, the transistor becomes saturated. The fuse latch circuit determines if a fuse is to be blown or electrically overridden.
Shamir, U.S. Pat. No. 5,384,559 discloses both an electrical plug and a spare fuse holder embodied within a single fire retardant plastic housing. The housing is configured to have a channel wherein a spliced electrical cord may be inserted with no danger of inadvertently making contact without being in series with the fuse element. The housing also contains two chambers: The first chamber has a cavity where the fuse element can be separately contained while being in series with the inserted conductor. A second chamber stores the replacement fuse so that it is not part of the circuit to be protected. The housing and its fuse chambers are shaped, positioned and constructed so that the replacement fuse need only be withdrawn from its storage chamber and inserted into the first chamber which formerly held the blown fuse. The chambers are formed to be easily opened to permit easy fuse replacement.
None of these previous efforts disclose all of the benefits of the present invention, nor do these previous patents teach or suggest all of the elements of the present invention.